Redox cycling of anthracyclines by cardiac mitochondria. II. Formation of superoxide anion, hydrogen peroxide, and hydroxyl radical

Increasing therapeutic effect and reducing toxicity of doxorubicin by N-acyl dehydroalanines

Doxorubicin toxicity is generally accepted to be free radical-mediated. N-Substituted dehydroalanines (indexed as AD compounds) are capto-dative olefins which react and scavenge free radicals, especially the superoxide anion (O2-) and hydroxyl radical (HO). AD-20, an orthomethoxyphenylacetyl dehydroalanine derivative, decreases the mortality of mice when administered before an acute single dose or multiple non-toxic doses of doxorubicin. Doxorubicin administered to mice induces elevated serum transaminase levels, and the pretreatment of mice with AD-20 decreases significantly these serum enzymatic activities. Preliminary histological examinations suggest that these serum transaminase elevations reflect most likely liver injury. In addition to its cardiotoxicity, doxorubicin induces a severe bone marrow depletion. Although this initial decrease in the peripheral leukocytes induced by doxorubicin is not prevented by the administration of AD-20, it produces a fast recuperation in the white blood cells levels after 1 week, supporting a protective effect at this level. Moreover, the antitumor effect of doxorubicin in L1210 tumor-bearing mice was enhanced when AD-20 was injected before doxorubicin. We postulate that these effects may be related to the free radical scavenging ability of AD-20.

Furazolidone-enhanced production of free radicals by avian cardiac and hepatic microsomal membranes

Furazolidone produces a dilative cardiomyopathy and hepatitis in turkeys exposed to this drug in their diets. The ability of furazolidone to enhance free radical reactions when incubated with turkey cardiac or hepatic membranes was determined to evaluate if free radical reactions might contribute to the pathology. Furazolidone (0.135 mM) incubated with NADPH and hepatic microsomes increased oxygen consumption 350% over control incubations. Superoxide dismutase and catalase attenuated the furazolidone-mediated stimulation of oxygen consumption, indicating that the drug promoted the formation of superoxide and hydrogen peroxide. Lipid peroxidation was also stimulated by furazolidone incubated with microsomes, NADPH, and ferric chloride. At concentrations as low as 0.017 mM, lipid peroxidation was more than doubled by furazolidone. Incubation of cardiac sarcosomes with NADPH and furazolidone (0.135 mM) increased oxygen consumption 72% the rate of cytochrome c reduction 72%, and epinephrine oxidation 238% over control. Epinephrine oxidation was enhanced by concentrations of furazolidone as low as 0.017 mM (69% increase over control). This effect of furazolidone was blocked by superoxide dismutase or incubation in an argon atmosphere. These data establish the potential for furazolidone to enhance free radical reactions in cardiac, as well as hepatic tissue. Free radical reactions are therefore potential determinants of furazolidone-mediated hepatic and cardiac toxicities.

The interaction of the cardioprotective agent ICRF-187 [+)-1,2-bis(3,5-dioxopiperazinyl-1-yL)propane); its hydrolysis product (ICRF-198); and other chelating agents with the Fe(III) and Cu(II) complexes of adriamycin

Membrane-permeable ICRF-187 [+]-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane) has shown promise as a cardioprotective agent against adriamycin-induced cardiotoxicity. ICRF-187 may act through its rings-opened hydrolysis product (ICRF-198), which has an EDTA-type structure and, likewise, strongly binds metal ions. The reactions of these compounds with Fe3+-adriamycin and Cu2+-adriamycin complexes were examined. ICRF-198 quickly and completely removed both Fe3+ and Cu2+ from their complexes with adriamycin. ICRF-187 also reacted directly, but more slowly, with Fe3+-adriamycin to remove Fe3+ from the complex. This reaction was first order in ICRF-187 and Fe3+-adriamycin and yielded a second order rate constant of 123 M-1 min-1. Metal ion-complex promoted hydrolysis may thus contribute to the in vivo hydrolysis of ICRF-187 to its metal ion-chelating active rings-opened form. Both ICRF-187 and ICRF-198 were very effective in preventing the Fe3+-adriamycin induced inactivation of the cytochrome c oxidase activity of submitochondrial particles. A number of other chelating agents (desferal; penicillamine; DTPA; EDTA; TPEN; bathophenanthroline sulfonic acid; 2,2'-bipyridine; 1.10-phenanthroline, glutathione and 2-mercaptoethanol) were also examined for their ability to remove Fe3+ and Cu2+ from their complexes with adriamycin.

Mechanism(s) of bioreductive activation. The example of diaziquone (AZQ)

Bioreduction in the activation of diaziquone (2,5-diaziridinyl-3,6-bis (carboethoxyamino)-1,4-benzoquinone) has been investigated by exploring its reduction by whole cells, rat liver microsomes and purified enzymes. The mechanism of bioreduction was further investigated by exploring the chemical and electrochemical reduction of diaziquone as well as its photochemistry. Reduced diaziquone (by several means) was then tested for activity against parent compound. It appears that reduced diaziquone in most cases is more active than the oxidized form. Diaziquone redox cycles, but it is easily reduced to the hydroquinone which oxidizes to the semiquinone yielding free radicals under aerobiosis. The most probable mechanism of action is that of bioreductive alkylation where the alkylating aziridines are protonated after reduction facilitating the opening of the aziridine rings and thus alkylation.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

gamma-radiolysis study of the reduction by COO- free radicals of daunorubicin intercalated in DNA

The reduction of daunorubicin intercalated in DNA was studied using COO- free radicals produced by gamma-radiolysis as reductants. The reduction process of the drug intercalated in DNA was found to be very similar to the one of daunorubicin in aqueous solution without DNA. (a) the final product is the same (7-deoxy daunomycinone); (b) the reduction yield is the same [2.6 +/- 0.2) x 10(-7) mol.J-1); (c) H2O2 reacts with hydroquinone daunorubicin giving back the drug in a one-step reaction. However 7-deoxy daunomycinone precipitation was so slow that this aglycone could be reduced by COO- free radicals giving its hydroquinone form, which cannot be observed without DNA. This shows that the whole 4-electron reduction process takes place in DNA. The implications of these findings are discussed.

Immobilized adriamycin: toxic potential in vivo and in vitro

We report experiments which test the toxicity of a new potential therapeutic agent, agarose-bound adriamycin (ImA). In C57Bl/6N mice this preparation is almost completely devoid of untoward effects when administered intraperitoneally; ImA lacks all the usual toxic repercussions of free adriamycin including abdominal adhesions, inflammatory peritonitis, weight loss and cardiotoxicity. The immobilized adriamycin is also inactive in a fetal mouse heart model of cardiac toxicity. This lack of toxicity is not due to an intrinsic inactivity of the drug, however, since previous studies have shown that polymer-bound adriamycin can kill actively dividing cells. We also show here that the immobilized drug can undergo redox reactions and interact with enzymes from isolated respiratory chain preparations, so the lack of cardiac toxicity in vivo is most likely due to inaccessibility of the target. These results suggest that polymer immobilized adriamycin lacks the toxicity of the parent compound and may present a useful approach to regional chemotherapy.

A new class of free radical scavengers reducing adriamycin mitochondrial toxicity

Beef heart mitochondria were incubated with ADM and NADH. An adriamycin semiquinone radical was detected using ESR spectroscopy. The semiquinone radical production rate is decreased upon addition of a scavenger (AD 20) in the reaction medium. NMRI mice were treated with AD 20 (70 mg/kg, i.p.) 15 min prior ADM injection (20 mg/kg, i.p.) or with ADM alone. Heart mitochondria were isolated 48 hr later. The enzymatic activities of complex I-III and complex IV of the mitochondrial respiratory chain were strongly depressed in animals receiving ADM alone, whereas these activities were almost completely restored in animals receiving AD 20 and ADM. Fluorescence depolarization measurements indicated that only mice treated with ADM alone presented a decreased fluidity of their cardiac mitochondrial membrane.

Evidence suggesting a role for hydroxyl radical in puromycin aminonucleoside-induced proteinuria

A single intravenous injection of puromycin aminonucleoside (PAN) results in marked proteinuria and glomerular morphological changes that are similar to minimal change disease in humans. We examined the effect of hydroxyl radical scavengers and an iron chelator on PAN-induced proteinuria. PAN in a dose of 5 mg/100 g body wt significantly increased urinary protein by day 5 (saline: 15 +/- 2, N = 24: PAN: 63 +/- 17, N = 23, P less than 0.001); the proteinuria rapidly increased thereafter, reaching 216 +/- 34, N = 23 by day 7. Concurrent administration of hydroxyl radical scavengers dimethylthiourea, (DMTU 500 mg/kg followed by 125 mg/kg i.p. twice a day) and sodium benzoate (BENZ, 150 mg/kg followed by 125 mg/kg i.p. twice a day) starting the evening before PAN injection markedly reduced proteinuria throughout the course of the study (urinary protein, mg/24 hours on day 7, mean +/- SEM: PAN: 229 +/- 45, N = 15; PAN + DMTU: 30 +/- 5, N = 18; PAN + BENZ: 80 +/- 18, N = 16. Because of the participation of iron in biological systems to generate hydroxyl radical, we also examined the effect of deferoxamine (DFO, 30 mg/day), an iron chelator, on the PAN-induced proteinuria. Concurrent administration of DFO was also protective. In a second series of experiments, DMTU and DFO (administered as described above and then for two additional days after the PAN) provided marked protection even when they were stopped prior to the onset of proteinuria. The protective effects of two hydroxyl radical scavengers and iron chelator implicate an important role for hydroxyl radical in PAN-induced nephrotic syndrome.

Adriamycin and its iron(III) and copper(II) complexes. Glutathione-induced dissociation; cytochrome c oxidase inactivation and protection; binding to cardiolipin

Some reactions of adriamycin (doxorubicin) and its Fe3+ and Cu2+ complexes were investigated with a view to understanding the mechanisms by which metal ion-adriamycin complexes damage cellular components. The ability of adriamycin in the presence of Cu2+ to inactivate the mitochondrial enzyme cytochrome c oxidase was effectively prevented by physiologic levels of glutathione. This result is explained by the observation that glutathione reacts with the Cu2+-adriamycin complex to produce free adriamycin. As sulfhydryl compounds are, in contrast, known to promote Fe3+-adriamycin-induced damage to cellular components, these results suggest that the response of a metal ion-adriamycin system to the presence of sulfhydryl compounds may be indicative of whether or not Cu2+-adriamycin is the damaging species. The partition of adriamycin into the octanol phase of an octanol-water two-phase system was greatly enhanced by the presence of cardiolipin. This result can be explained by the formation of a strong adriamycin-cardiolipin complex in the octanol phase which is one-half formed at an adriamycin concentration of 6 microM.

Adriamycin-induced lipid peroxidation in mitochondria and microsomes

The effect of the anti-neoplastic agent adriamycin on the peroxidation of lipids from rat liver and heart mitochondria and rat liver microsomes was investigated. The extent of total lipid peroxidation was determined by assaying for malondialdehyde (MDA), while the degradation of unsaturated fatty acids was monitored using gas chromatography. For liver mitochondria and microsomes, the formation of MDA was dependent on the concentrations of adriamycin, Fe3+, and protein, as well as time. In the presence of 50 microM adriamycin and saturating amounts of NADH, 1.5 +/- 0.2 nmol MDA/mg protein/60 min was produced with liver mitochondria. Upon addition of 25 microM Fe3+, the amount of MDA generated was increased to 6.5 +/- 0.1 nmol/mg protein/60 min. Liver microsomes produced amounts which were approximately 2-fold higher under all conditions. No MDA formation could be detected in rat heart mitochondria. The addition of 50 microM chlorpromazine completely inhibited peroxidation, whereas 0.5 to 1.0 mM p-bromophenacyl bromide blocked MDA formation by 50%. Analysis of fatty acids by gas chromatography showed that there was about a 50% decrease in arachidonic and docosahexaenoic acids in liver mitochondria and microsomes, but no change in the fatty acid content of heart mitochondria when incubated with both 50 microM adriamycin and 25 microM Fe3+ for 1 hr. These results suggest that (1) therapeutic concentrations of adriamycin enhance the peroxidation of lipids in liver mitochondria and microsomes through an enzymatic mechanism, especially in the presence of Fe3+; and (2) toxicity of this drug may be related to the degradation of membrane lipids.

DNA damage and oxygen radical toxicity

A major portion of the toxicity of hydrogen peroxide in Escherichia coli is attributed to DNA damage mediated by a Fenton reaction that generates active forms of hydroxyl radicals from hydrogen peroxide, DNA-bound iron, and a constant source of reducing equivalents. Kinetic peculiarities of DNA damage production by hydrogen peroxide in vivo can be reproduced by including DNA in an in vitro Fenton reaction system in which iron catalyzes the univalent reduction of hydrogen peroxide by the reduced form of nicotinamide adenine dinucleotide (NADH). To minimize the toxicity of oxygen radicals, the cell utilizes scavengers of these radicals and DNA repair enzymes. On the basis of observations with the model system, it is proposed that the cell may also decrease such toxicity by diminishing available NAD(P)H and by utilizing oxygen itself to scavenge active free radicals into superoxide, which is then destroyed by superoxide dismutase.

Direct detection of paramagnetic species in adriamycin perfused rat hearts

Direct detection of paramagnetic species in control and adriamycin-perfused rat hearts has been carried out. Depending on the flow rate of the perfusion solution (8,4,2 and 1 ml/min) different paramagnetic species were observed: Fe(III)(g = 2.12) at 4 ml/min; three types of oxygen centered radicals of which two in control hearts (g = 2.05 g = 2.038 g = g = 2.008) and the third one (g = 2.03 g = 2.005) in adriamycin perfused hearts, at 2 ml/min. The latter radical was the only one observed at perfusion rate of 1 ml/min both in control and adriamycin treated systems. A relationship between the intracellular enzymatic reductive activation of the anthracycline and the occurrence of ischemic conditions (4,2 and 1 ml/min) in myocardial tissues is proposed basing on the relative amounts of the paramagnetic species above mentioned.

Gentamicin enhanced production of hydrogen peroxide by renal cortical mitochondria

Agents that affect mitochondrial respiration have been shown to enhance the generation of reactive oxygen metabolites. On the basis of the well-demonstrated ability of gentamicin to alter mitochondrial respiration (stimulation of state 4 and inhibition of state 3), it was postulated that gentamicin may enhance the generation of reactive oxygen metabolites by renal cortical mitochondria. The aim of this study was to examine the effect of gentamicin on the production of hydrogen peroxide (measured as the decrease in scopoletin fluorescence) in rat renal cortical mitochondria. The hydrogen peroxide generation by mitochondria was enhanced from 0.17 +/- 0.02 nmol . mg-1 . min-1 (n = 14) in the absence of gentamicin to 6.21 +/- 0.67 nmol . mg-1 . min-1 (n = 14) in the presence of 4 mM gentamicin. This response was dose dependent with a significant increase observed at even the lowest concentration of gentamicin tested, 0.01 mM. Production of hydrogen peroxide was not increased when gentamicin was added to incubation media in which mitochondria or substrate was omitted or heat-inactivated mitochondria were used. The gentamicin-induced change in fluorescence was completely inhibited by catalase (but not by heat-inactivated catalase), indicating that the decrease in fluorescence was due to hydrogen peroxide. Thus this study demonstrates that gentamicin enhances the production of hydrogen peroxide by mitochondria. Because of their well-documented cytotoxicity, reactive oxygen metabolites may play a critical role in gentamicin nephrotoxicity.

Effects of adriamycin on respiratory chain activities in mitochondria from rat liver, rat heart and bovine heart. Evidence for a preferential inhibition of complex III and IV

The inhibition of respiratory chain activities in rat liver, rat heart and bovine heart mitochondria by the anthracycline antibiotic adriamycin was measured in order to determine the adriamycin-sensitive sites. It appeared that complex III and IV are efficiently affected such that their activities were reduced to 50% of control values at 175 +/- 25 microM adriamycin. Complex I displayed a minor sensitivity to the drug. Of the complex-I-related activities tested, only duroquinone oxidation appeared sensitive (50% inhibition at approx. 450 microM adriamycin). Electron-transfer activities catalyzed by complex II remained essentially unaltered up to high drug concentrations. Of the activities measured for this complex, only duroquinone oxidation was significantly affected. However, the adriamycin concentration required to reduce this activity to 50% exceeded 1 mM. Mitochondria isolated from rat liver, rat heart and bovine heart behaved essentially identical in their response to adriamycin. These data support the conclusion that, in these three mitochondrial systems, the major drug-sensitive sites lie in complex III and IV. Cytochrome c oxidase and succinate oxidase activity in whole mitochondria exhibited a similar sensitivity towards adriamycin, as inner membrane ghosts, suggesting that the drug has direct access to its inner membrane target sites irrespective of the presence of the outer membrane. By measuring NADH and succinate oxidase activities in the presence of exogenously added cytochrome c, it appeared that adriamycin was less inhibitory under these conditions. This suggests that adriamycin competes with cytochrome c for binding to the same site on the inner membrane, presumably cardiolipin.

Intracellular proteolytic systems may function as secondary antioxidant defenses: an hypothesis

In recent years it has become clear that various free radicals and related oxidants can cause serious damage to intracellular enzymes and other proteins. Several investigators have shown that in extreme cases this can result in an accumulation of oxidatively damaged proteins as useless cellular debris. In other instances, proteins may undergo scission reactions with certain radicals/oxidants, resulting in the direct formation of potentially toxic peptide fragments. Data has also been gathered (recently) demonstrating that various intracellular proteolytic enzymes or systems can recognize, and preferentially degrade, oxidatively damaged proteins (to amino acids). In this hypothesis paper I present evidence to suggest that proteolytic systems (of proteinases, proteases, and peptidases) may function to prevent the formation or accumulation of oxidatively damaged protein aggregates. Proteolytic systems can also preferentially degrade peptide fragments and may thus prevent a wide variety of potentially toxic consequences. I propose that many proteolytic enzymes may be important components of overall antioxidant defenses because they can act to ameliorate the consequences of oxidative damage. A modified terminology is suggested in which the primary antioxidants are such agents as vitamin E, beta-carotene, and uric acid and such enzymes as superoxide dismutase, glutathione peroxidase, and DT-diaphorase. In this classification scheme, proteolytic systems, DNA repair systems, and certain lipolytic enzymes would be considered as secondary antioxidant defenses. As secondary antioxidant defenses, proteolytic systems may be particularly important in times of high oxidative stress, during periods of (primary) antioxidant insufficiency, or with advancing age.

Reduction of oxygen by NADH/NADH dehydrogenase in the presence of adriamycin

Cardiac mitochondrial NADH dehydrogenase (Cytochrome c reductase, EC1.6.99.3) catalyses the reduction of ferricytochrome c to ferrocytochrome c by NADH. In the presence of the anthracycline anti-tumour drug, adriamycin, electron transfer from NADH is subverted to dioxygen. Using the electron spin resonance technique of spin trapping with the spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) adriamycin was found to stimulate the formation of superoxide and hydroxyl radicals in the NADH/NADH dehydrogenase reaction. Hydroxyl radical formation is dependent on the availability of trace amounts of redox active metal ions - particularly ferric ions. Trace amounts of ferric ions catalyse the formation of hydroxyl radicals by both superoxide-dependent and adriamycin-dependent one electron reduction of hydrogen peroxide. The metabolism of adriamycin by cardiac mitochondrial NADH dehydrogenase may be an important etiological factor in adriamycin-induced cardiotoxicity. It may be therapeutically beneficial to keep nonessential ferric/ferrous ions in the myocardium at minimum levels with siderophoric iron chelators - providing the anti-tumour activity of adriamycin is not impaired.

Pulse radiolysis study of daunorubicin redox reactions: redox cycles or glycosidic cleavage?

Two aspects of daunorubicin reactivity were investigated by pulse radiolysis. The reactions of O2 and O2- with the semiquinone and the hydroquinone transients of daunorubicin were determined and their rate constants measured. Although O2- can reduce the drug and its semiquinone form, it is a more powerful oxidant towards the two reduced transients. The hydroquinone daunorubicin glycosidic cleavage in aqueous solution was studied. Three intermediates were seen and characterized by their absorption spectra, their formation and decay kinetics. The competition between these two main processes was evaluated in the conditions of pulse radiolysis. Even under low O2 partial pressures the redox cycles are much more rapid than the glycosidic cleavage and a relatively high O2- steady state is settled. Biological implications are discussed.